英文:
Why does math/rand return the same result every time I restart my program?
问题
我有点困惑。我有一个随机字符串生成器，以下是代码：
package utilsimport ("fmt""math/rand")var chars = []rune("abcdefghijklmnopqrstuvwxyz0123456789")func RandSeq(n int) string {b := make([]rune, n)for i := range b {b[i] = chars[rand.Intn(len(chars))]}fmt.Println(string(b))return string(b)}
每次运行这段代码时，它都会生成一个新的随机字符串，但是如果我重新启动服务器，结果会重复。以下是一些结果：
go run main.gofpllngzieyoh43e0133ols6k1hh2gdnyxxvi7hvszwk1b182tvjzjpezi4hx9gvmkir0xcta0opsb5qipjzb3h3x9kcegta5m1zcv5drxckn42gb50anxndsckjdwgfw5japz01zicapy9eqixuc9uehq235v48c51wgg1gypq4s9miwn1dxkjqd614m58f0fyy29g6ujmxbouxshy2plmkmhlnmdbfhf7kq8u26873eql4yyp7fyilbb72nrtlcgo run main.gofpllngzieyoh43e0133ols6k1hh2gdnyxxvi7hvszwk1b182tvjzjpezi4hx9gvmkir0xcta0opsb5qipjzb3h3x9kcegta5m1zcv5drxckn42gb50anxndsckjdwgfw5japz01zicapy9eqixuc9uehq235v48c
有任何想法为什么会发生这种情况吗？
英文:
I'm a little confused. I have a random string generator, here's the code:
package utilsimport ("fmt""math/rand")var chars = []rune("abcdefghijklmnopqrstuvwxyz0123456789")func RandSeq(n int) string {b := make([]rune, n)for i := range b {b[i] = chars[rand.Intn(len(chars))]}fmt.Println(string(b))return string(b)}
Every time I run this, it will generate a new random string, but if I restart the server the results will repeat themselves. Here are some results:
go run main.gofpllngzieyoh43e0133ols6k1hh2gdnyxxvi7hvszwk1b182tvjzjpezi4hx9gvmkir0xcta0opsb5qipjzb3h3x9kcegta5m1zcv5drxckn42gb50anxndsckjdwgfw5japz01zicapy9eqixuc9uehq235v48c51wgg1gypq4s9miwn1dxkjqd614m58f0fyy29g6ujmxbouxshy2plmkmhlnmdbfhf7kq8u26873eql4yyp7fyilbb72nrtlcgo run main.gofpllngzieyoh43e0133ols6k1hh2gdnyxxvi7hvszwk1b182tvjzjpezi4hx9gvmkir0xcta0opsb5qipjzb3h3x9kcegta5m1zcv5drxckn42gb50anxndsckjdwgfw5japz01zicapy9eqixuc9uehq235v48c
Any idea why this is happening?
答案1
得分: 8
你需要在生成任何随机数之前，先对随机数生成器进行种子。一个好的值可以使用当前的Unix时间戳：
import ("math/rand""time")func main() {rand.Seed(time.Now().UnixNano())}
请注意，你应该只在启动时（或分叉后）对随机数生成器进行一次种子操作，而不是在每次生成随机数之前都进行种子操作。
英文:
You need to Seed the random number generator prior to generating any random numbers. A good value to use is the current unix timestamp:
import ("math/rand""time")func main() {rand.Seed(time.Now().UnixNano())}
Note that you should only seed the RNG once at startup (or after forking), not before each random number generation.
答案2
得分: 2
如果未设置rand.Seed，它会将种子默认设置为1，导致每次生成相同的随机数。
在启动时使用一个随机数种子来初始化rand，例如rand.Seed(time.Now().UnixNano())，将使得每次运行程序时都得到不同的结果。
你也可以创建自己的随机变量，例如：
var random = rand.New(rand.NewSource(time.Now().UnixNano()))func main() {num := random.Intn(10)fmt.Println(num)num = random.Intn(10)fmt.Println(num)}
英文:
If rand.Seed is not set, it defaults the seed to 1, giving you the same random number every time.
Seeding rand at startup with a random number like rand.Seed(time.Now().UnixNano()) will give you a changing result each time you run your program.
You can also create your own random var like:
var random = rand.New(rand.NewSource(time.Now().UnixNano()))func main() {num := random.Intn(10)fmt.Println(num)num = random.Intn(10)fmt.Println(num)}
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